1. Field of the Invention
This invention relates to an apparatus for determining the rotational velocity of a rotary shaft. More particularly, this invention relates to an apparatus for mounting a transducer on a rotating shaft for detecting and measuring the rotational velocity of the shaft.
2. Description of the Prior Art
Of prior art apparatus for measuring the rotational velocity of a rotary shaft, one such apparatus is a rotational signal transducer. The transducer is mounted in a fixed position adjacent gear teeth of a gear which is fixed to the shaft. An apparatus for mounting a transducer adjacent gear teeth is shown in Bulletin 11007B, Speed Signal Generator, of the Woodward Governor Company, Rockford, Ill.
Such transducers are typically provided with a magnetic core. As the shaft and connected gear rotate, the gear teeth passing the transducer produce a change in the magnetic field about the core. Responsive to the change in the magnetic field, the transducer generates a signal having a frequency proportional to the rotational speed of the shaft. The signal is translated to provide a reading of the rotational velocity of the shaft.
One problem associated with rotational signal transducers results from axial movement of the shaft. As the shaft moves axially with relative movement between the gear and the transducer, the relative movement is detected by the transducer with a resulting modification in the generated signal. Consequently, axial movement of the shaft, even though very slight, results in a misleading reading of the rotational velocity of the shaft.
To overcome the problems associated with axial movement of the shaft, sophisticated apparatus such as described in the aforementioned bulletin, have been developed to mount the transducer over the gear teeth to avoid deceptive readings resulting from shaft axial movement. While such prior art apparatus are generally adequate for providing a reliable signal of the shaft's rotational velocity, the apparatus is typically complicated to maintain and must be located at an end of the rotary shaft. In certain applications, such as for measuring the rotational velocity of a turbine shaft in a horizontal bulb-type hydraulic turbine, critical space limitations prevent the apparatus from being located at the end of the shaft.